The mechanism of intracellular pH regulation in isolated perfused renal tubules and epithelial cells in culture is under investigation. We are using a unique fluorescent pH probe, 1,4 Dihydroxyphallonitrile, which has both a fluorescent acid (blue) and base (green) form. This probe in a cell used in combination with a rapid scanning microfluorometer on a microscope permits the topological assessment of intracellular pH. Currently we are studying the mechanisms of intracellular proton buffering mechanisms with regards to external and intrinsic acid loads.